Twist type chuck



May 3, 1960 E. NlcKoLAlsEN 2,935,328

TWIST` TYPE cHucx Filed Jan. 31, 1958 2 Sheets-Sheet 2 IN VEN TOR.

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United States Patent() 2,935,323 iwrsr TYPE CHUCK Elmer Nickolasen, Venice, Calif. Application January 31, 1958, Serial No. 712,555

2 Claims. (Cl. 279-46) This invention relates to chucks which can be employed for various work piece holding purposes, and has been devised to be especially useful for grasping and holding the end of a tube which is undergoing a series of bend operations in a tube bending machine.

The chuck of the present invention has been particularly designed to be used in conjunction with the tube bending machine shown in United States Patent No. 2,382,745, issued August 14, 1945, to Douglas Aircraft Company, lnc. as assignee of Marvin A. Powers.

In general a tube bending machine consists essentially of a means for holding a tube for rotational and lengthwise movement, and a bending device positioned along the path of the lengthwise movement of the tube'for making one or a series of bends therein. The spacing between successive bends is obtained by moving the tube lengthwise the desired distance. The angle between the planes of successive bends is obtained by rotating the tube preparatory to making a later bend of a series of bends until the rst formed bend of the series makes the desired angle with the plane of the bender. rihe degree of arc of each bend is determined by turning the radius block of the bending device until it has travelled about its axis through the desired arc.

lt is essential that a tube bending machine have adequate means for holding the trailing end of the tube as it is fed to the bending device without deformation of the tube, and in a manner which permits the making of a bend closely proximate the trailing end of the tube, thereby eliminating waste of stock beyond the last bend. The present invention is designed to provide improved means tor holding the tube for rotational and lengthwise movement and for feeding it step by step to the bending device.

Presently available chucks for use with tube bending machines, and particularly the tube bending machine of Patent No. 2,3 82,745, have several inherent disadvantages. To operate the machine there disclosed, a tube is rst inserted between a clamping block and radius block and passed over a mandrel and positioned with its trailing end in the unclarnped jaws of a chuck. A carriage upon which the chuck is mounted is then moved rearwardly against a stop, this contact actuating the clamping jaws ot the chuck, causing them to tightly grip the trailing end of the tube. ln operation, the carriage is normally moved by the operator at a fairly rapid rate to insure operation of the mechanism which actuates the clamping jaws. This has resulted in considerable damage to the chuck itself, thus necessitating many changes and repairs, causing considerable spare part expense, and increasing the down-time of expensive machinery.

As previously pointed out, the chuck of the present invention has been designed for use with the bending machine described in the Powers patent. To appreciate its application to this machine, it is desirable to have some knowledge of the construction and operational sequence of the Powers bender. Y i

When the tube has been gripped as described herein- Patented May 3, 1960 above, the machine is then in its initial position to make the rst bend in the tube. To select the points along the length of the tube where the several bends are to be made, a series of adjustably positioned stops are provided on a stop rail attached to the Powers machine. The tube and carriage are pulled forward, from the above men; tioned initial position, until a pawl rides over and passes the rst of the stops. The operator then backtracks the tube and carriage until the rear face of the pawl strikes the front face or" the stop, in which position the machine is ready for making the iirst bend in the tube. In a similar manner the carriage and tube are successively set for makingrthe remaining bends.

The angular ,spacings of the planes of the bends in a tube are determined by a plurality of slip rings rotatively slidable upon a bender drum. Each slip ring is provided with an outwardly extending lug which, when the slip ring is rotated, moves across the path of longitudinal movement of a stop lug carriedon a slide block. The machine is prepared for operation by setting the rst or leading slip ring on the bender drum with its lug in contact with `one side or the other of the stop carried by the slide block. A pawl is then manually operated to permit an escapement mechanism to move the Stop ,lug to the vertical plane of the second or next rearward slip ring on the bender drum. T he drum is then rotated either clockwise or counter-clockwise to move the lug of the leading slip ring away from the stop lug, depending upon which side of the stop is contacted by the lug, until the desired angle is achieved. The second slip ring is then turned in the same direction to bring the advancing face of its lug against the stop. The slip ring is then clamped to the bender drum. The remaining slip rings are `similarly set, one slip ring for each bend in the tube. The slip rings then determine the degree of each bend, the first or leading ring correspond ing to the rst bend and each ring being set on the drum with the advancing face of its lug contacting the stop lug when the desired angle has been turned. When the tube has been clamped as hereinabove pointed out, the tube clutch and drum are then rotated until the lug on the rst slip ring is against the same side of the stop lug as that used in setting the machine. The iirst bend is then made and the tube moved to the next position. An escapement mechanism causes the slide block carrying the stop to move to a second position in line with the second lug carrying slip ring carried on the bender drum. Again the tube, clutch, and drum are rotated until the slip ring lug engages the stop. The bender clamps are again set and the bender arm is pulled to make the second bend. Upon completion of the last bend and release of the bender clamps, the carriage and tube are pulled forward until a limit stop trips. In some chucks heretofore available for use in conjunction with the Powers bending machine, the operator pushes down on a gripper handle and releases the clutch jaws from the tube. The tube is then removed from the machine and the bender arm returned to its initial position.

Several important aspects of the above operational sequence should be noted. When the tube is loosely inserted between the separated chuck jaws and the carriage is pushed tailwardly, the projecting end of a sleeve contacts a stop which projects headwardly from a movable stop carriage which can be selectively clamped at any desired position. This contact, as previously pointed out, causes the chuck jaws to become ready for the bending operation by firmly clamping the end of the tube. To insure operation of the chuck, it is necessary for the operator to move the carriage rearwardly with force enough to Contact the stop rmly. As indicated, this has caused considerable damage to the fairly delicate operating mechanism' of previous chucks. 'I'he present invention completely eliminates this problem by providing a tube chuck which is operable with a slight twisting motion to firmly grip the trailing end. of the tube preparatory to the actual bending operation.

Many of the tube gripping devices heretofore available for use in connection with tube benders, such as the Powers machine,rhave been characterized by additional deficiencieswhich hampered the eicient utilization of the machine by the operator. This is particularly true in connection with the procedure to be taken by the operator just prior to making the last bend yin the tube. If the bend is to occur relatively close to the trailing end of the'tube, as it often'does, the chuck assembly must be pulled forward a relatively long distance. This many times results in a portion of the assembly overlapping the end of the clamping block. If the chuck has a protruding or extending portion, such as the clamping handle provided on some of the presently available gripping devices, the clamping block will stop the forward motion of Ythe chuck unless the, protruding portion is in a position so as not to interfere with the clamping assembly. Because the position of the extension is determined by the plane of the final bend, it is not practicable to set the chuck so that the extension will always be clear of the clamping assembly when the tube is pulled Yforward to the final bend position. It is therefore many times necessary to loosen the chuck assembly and rotate the handle or extending portion until it clears the clamping block before the tube can be pulled forward in position for the final bend.

In some chucks, heretofore available, which utilize an extending handle to grip and release the tube, it was, at times, extremely difficult to release the tube for, as previously indicated, the position of the handle, when'the tube was in place for the final bend, depended upon the plane of the final bend, and, because of this, the releasing handle was, many times, in a position where the operator could not grasp it firmly enough to actuate the releasing mechanism. Here again the chuck assembly would have to be loosened and rotated until the handle was in a position which would permit the operator to obtain a firm releasing grip. It should be understood that when the final bend occurs at a point near the trailing end of the tube, it is necessary to release the tube just before the final bend takes place to permit the end of the tube to slide by the clamping and bending dies as the bender arm is turned.

Again the provision of a tube chuck utilizing a simple twist motion to grip and release obviates these inconveniences. This is so for there is no extending portion or. gripper arm to interfere with the clamping die and the tube can be released easily from whateverposition it may be in at the time the final bend is to be made.

It should also be noted'that in operating the Powers machine it is necessary to continually rotate the bender drum in the same direction to insure that the various slip rings contact the stop lug at the proper positions. Thus to obtain ease of operation, the operator should be able to place the trailing end of the tube in the unclamped jaws of the chuck and twist the chuck untilthe slip ring lug engages the stop lug. The operator then continues turning in the same direction until the chuck clamps. It is also essential that, when the tube has been placed in position just prior to the final bend operation, the release motion be in the same direction of rotation as that positioning the final slip ring lug against the stop. This, then, necessitates that both gripping and releasing actions to the final bend operation without necessitating any inconvenient and time consuming adjustment of the chucks position.

Other features and advantages of the present Yinvention will be apparent from the following description taken in connection with the accompanying drawing in which:

Figure l is an elevation View in section of the chuck of the present invention showing the end of a tube inserted in the gripping portion, and the chuck being shown in operative position firmly clamping the end of the tube;

Figure 2 is a view similar to Figure 1 but showing the chuck in unclamped position;

Figure 3 is a perspective view of part of the operating mechanism shown in Figures l and 2;

Figure 4 is a perspective View of one portion of the cammingA mechanism shown in Figures l and 2;

Figure 5 is a view similar to Figure l but showing a modified form of the chuck of the present invention in clamping operation; Y

Figure 6 is a view similar to Figure 5 but showing the chuck in unclamped position; and Figure 7 is a perspective view partly broken away of a portion of the clamping mechanism shown in Figures 5 and 6.

Referring now to the drawing and more particularly to Figures l to 4 thereof, there is shown a chuck 12 which includes a Ytubular housing or casing 13 with an internal bore 14. The exterior surface 15 of housing member 13 is gripped by the operator when actuating the chuck to clamp or unclamp the workpiece. The outer surface 15 may therefore be substantially cylindrical in cross section and knurled to insure a firm grip. However, it is now preferred in the embodiment presently being described to use a handle wherein the outer surface is substantially hexagonal in cross section thus enabling the operator to secure the necessary grip. It has also been found in actual operation that a handle of such configuration can be used for long periods of time without chang or blistering the operators hands. The interior of handle 13 is formed as a cylindrical bore 14 for retaining a portion of the operating mechanism of the chuck. The forward end of tubular housing 13 is provided with an inwardly extending flange or lip 17 which serves as a retaining 'shoulder 18 for cam member 19. Cam 19 is shown in perspective in Figure 4 and comprises an annulus formed with a flat side 20, the opposite side 22 being formed with a cammed surface constructed to mate, referring now particularly to Figure 3, with the cammed surface 23 of a second annulus 24 mounted on sleeve 25. The annulus 19 is a press or force lit in internal bore 14 and when installed is forced firmly against abutting shoulder 18, thus insuring that it will not rotate relative to housin 13.

hollow shaftor support member 27 passes through Y the two openings 28 and 29 provided at each end of be accomplished by actuating the chuck in the same dihandle 13. Shaft or support member 27 is internally threaded as shown at 30 at its forward end to receive the externally threaded portion 32 of collet or gripper jaw 33. kBearing 34 permits housing member 13 to rotate relative to shaft 27. A cup shaped internal sleeve 35, shown in perspective in Figure 3, is attached at one end 37 to shaft 27 and is mounted wholly within and concentric with handle member 13 and is rotatable by means of bearing 34 with respect to said'handle. Sleeve 35 is also concentric with respect to shaft 27, extending forwardly of'its Vattachment point 37 to define a compression spring receiving spaceY 38.` A longitudinally extending slot 39 is provided in internal sleeve 35 insuring proper mating engagement with external sleeve member 25 by means of guide lug 40. One end portion of sleeve 25 extends to a position outside of housing member 13 and is attached toy 'an actuating sleeve or collar 42 by means of Ycollar and set screw 43. The opposite end 44 of sleeve 25 extends within internal sleeve V35 va distance determined by the length of the longitudinally extending slot 39, A cammed surface Vannulus 24 surrounds and ansa-ses is 'attached to external sleeve 25. A compression spring 47, in surrounding relationship to shaft 27 is positioned within inner sleeve member 35. One end 48 of spring 47 is seated against the inside of the closed end of internal sleeve 35, the other end abutting against inner end 50 of external sleeve 2S thus forcing sleeve 25 to the left until the camming surfaces 23 and 22 meet and resist further movement.

The construction of the chuck can readily be seen when the assembly procedure is studied. When cam 19 has been installed in housing member 13, external sleeve member 25, with cam annulus 24 attached or made integral therewith, is slipped into position by inserting it in the right hand opening 29 of housing 13 as shown in Figures l and 2. Compression spring 47 is then slid into position from the left on shaft 27 as viewed in Figures l and 2 until it abuts against the inside face ofinternal sleeve member 35 which has been previously attached to or made integral with shaft 27. Shaft 27 with sleeve 3S attached thereto is then inserted through the same opening in housing 13 as was external sleeve 25 and rotated until guide lug 4@ mates with slot 39 provided in sleeve 35. of shaft 27 as shown in Figures l and 2 and retainer `slip ring 52 installed in the inside peripheral groove 53 provided in housing 13, thus locking the unit together. After actuating sleeve 42 has been positioned in the end `of outer sleeve and locked by means of set screw and collar 43, collet 33 is threaded into the internally threaded aperture provided in tube 27.

When thus assembled and suitably attached to a tube .bending machine, suc'n as, for example, the Powers bending machine, the chuck is ready for operation. With the vchuck in its unclamped position, as shown in `Figure 2, a tube 55 is inserted between a clamping block and radius block and passed over a mandrel and mandrel rod and positioned with its trailing end in the loosely related opposite jaws of collet 33. The outer housing member 13 is then gripped by the operator and rotated in a predetermined direction, either clockwise or counterclockwise as the previous setting of the bending machine requires. As the tubular housing 13 rotates, it carries with it the annulus 19 which has been firmly pressed into position against abutting shoulder 1'8 as previously described.

It should be understood that as the handle 13 is rotated by the operator, carrying with it annulus 19, the exterior sleeve member 25 is also rotated. This is readily apparent for sleeve 25 is either suitably attached to, or made integral with, the second cammed annulus 24 which has its cammed face 23 forced by the action of spring 38 into firm contact with the mating cammed surface 22 of annulus 19. By reason of the frictional drag developed by the biasing action of spring 47 coupled with the partially interlocking mating configuration of the cammed surfaces 22 and 23, annulus 19 carries with it annulus 24 which in turn rotates external sleeve 25. Collar and set screw 43 insure that the actuating sleeve 43 rotates with the sleeve 25. Internal sleeve 35, by means of lug 4G and longitudinal slot 39', also rotates with the outer housing 13, and in turn carries with it shaft 27 and collet 33. Thus as the operator initially rotates the handle 13, the entire chuck assembly also rotates.

When the handle has been rotated a predetermined distance, a stop, as for example that previously described when discussing the Powers bending machine and as fully set out and illustrated in U.S. Patent No. 2,382,745, is provided, which prevents further rotation of shaft 27 and its associated parts. The operator, however, continues to rotate handle 13 causing the mating cammed surfaces 22 and ..3 to rotate relative to one another; that is, the annulus 19 continues to rotate while annulus 24 is held stationary. Assuming that the chuck is initially in the .uncl'arnped position shown in Figure 2, the cammed surfaces are so designed that as they move relative to one Bearing 34 is then slid over the right end.

6 another, the action of compression spring 38 against 'the inner end 5G of sleeve 25 causes the sleeve to move to the left as shown in Figure l. This in turn causes actuating sleeve 43 to move longitudinally relative to collet 33, thus causing the opposing jaws of collet 33 to rmly clamp the trailing end of tube 55.

With the tube clamped firmly, the machine is now set for bending the tube in a prescribed pattern. The rst bend is made and the tube pulled forward to the next position as previously described. Upon completion of the last bend, if it is suihciently far from the trailing end of the tube, and upon release of the bender clamps, the tube is released from the jaws of the chuck and removed from the machine. However, if the last bend is to take place relatively near to the trailing end of the tube, it is necessary to release the tube before the nal bend is accomplished, for as the bender arm is pulled to make the last bend, the end of the tube must be free to slide by the clamping and radius blocks.

ln the present invention the operation to release the tube is the same whether it is done before or after the iinal bend. However, these two alternate sequence procedures for releasing the tube `are important to fully understand the function and advantages of the present tube chuck.

vIf it is necessary to release the tube before the nal bend is made, it should be understood that the handle has been rotated until some portion of the chuck mechanism abuts yagainst a stop, this position then determining the plane of the final bend. It is essential then that the' tube remain in that exact position and that the release action does not disturb it. The present chuck is well adapted to perform this function for it will permit the tube to be released by continuing to turn the handle in the same direction which carried the mechanism into the stop. rIhus although the tube is released, it still retains its final set position.

This is readily understood for as the rotation of shaft 27 is prevented and the operator continues to turn the handle, the mating surfaces 22 and 23 again move relative to one another. They are so designed that such relative movement causes the annulus 24 to move back against the biasing action of spring 3S and in turn, as previously pointed out, carrying with it actuating sleeve 42, thus permitting the opposed jaws of collet 33 to return to their loosely related or unclamped position. The tube can then be withdrawn from the jaw.

lt should be understood that the word tube as used herein includes pipes and other hollow or solid elongated objects of circular or other cross sectional configuration so characterized structurally that they may be gripped by a chuck constructed in accordance With this invention.

Certain variations in the specific design disclosed hereinabove are believed obvious without departing from the principles of the invention. Such a modification of the chuck is shown in Figures 5 to 7.

The tube chuck there shown consists of a hollow shaft or support member 53 adapted at one end 59 for attachment to a tube bending machine and threaded internally at its opposite end 62 to receive the externally threaded portion of collet 64. Either made integral with, or tixediy secured to, shaft 5S is sleeve bolt 65 formed with an externally threaded cylindrical portion 67 which terminates at one end in an enlarged flan-ge portion 68. A cylindrical sleeve 69 is internally threaded at one end for attachment to member 65, the end of sleeve 69 abutting against the inside face of flange 68 when the sleeve has been threaded down tightly.

The wall thickness of sleeve 69 decreases at 73 thus forrninfT a shoulder which divides the external portion of sleeve 69 into two sections 74 and 75, one having a larger diameter than the other. The smaller or right hand portion as shown in Figures 5 and 6 is internally threaded as at 78 and isy provided, at a point intermediate its length, with a longitudinally Aextending slot 77. l A compression coil spring '79 in surrounding relationship to shaft 58 with one end Si) seated against the end of member 65 and the opposite end abutting the end of internal sleeve member 83 normally urges sleeve S3 to the right.V A heavyduty screw S passes 4through Vslot 77 and is threaded into the slightly flanged end of sleeve 83. An actuating sleeve or collar S3 mounted in surrounding relationship to collet 64 is attached to the right end of sleeve 83 by means of collar and set screw 90.

A knurled handle 92, concentric with shaft 53 and the smaller portion 75 of sleeve 69 has its inner end abutting against shoulder 93 and is held trmly in place by internallyY threaded annulus 94 which is threaded down on the externally threaded portion 95 of sleeve 69. A sleeveY 97, shown in perspective in Figure 7, with a cammed surface 98 Ycontacting' the cap of screw 85 is mounted within handle 92 and held firmly in place by set screw 99. To insure stability of the handle 92 spacer sleeve 100 substantially ills the annular space between handle 92 and the smaller portion 75 of sleeve 69 just axially adjacent sleeve 97. A sleeve bolt 14M threads into the internally threaded portion 103 of sleeve 69 and acts as a sliding bearing permitting sleeve 33 to longitudinally reciprocate under the combined action of cammed surface 98 and spring 79.

The construction of this embodiment of the tube chuck may be readily seen from an examination of the assembly procedure. After sleeve bolt 65 has been properly placed, cylindrical sleeve 69 is slipped into place, from the right as shown in Figures 4 and 5, on hollow shaft 58 and threaded down tightly with one end firmly abutin-g-again'st iiange 68. Spacer member iii@ is then positionedon sleeve 69 against shoulder 93. Compression spring 79 is then slid into position on shaft 58 with one end abutting the inner end of sleeve bolt 65. Internal sleeve 83 is next slipped over shaft 5S, thus compressing spring 79, and into cylindrical sleeve 69 and rotated until the threaded hole 113 in its flanged end is aligned with the longitudinal slot 77 in sleeve 69. Screw 85 is then inserted through slot 77 into -threaded hole 113, thus retaining external sleeve 83 on shaft 5S against the biasing action of spring 79. Cam sleeve 97 is then placed in position in handle 92 and set screws 99 are inserted to hold it rmly in place. Handle 92 is then positioned over spacer sleeve 198 and held iirmly against shoulder 93 by screwing internally threaded annulus 94 on the externally threaded end portion of cylindrical sleeve 69. Sleeve bolt 97 is then threaded into the internally threaded end portion of sleeve 69, after which the rearwardly extending portion 115 of actuating sleeve 8S is placed inside the end portion of sleeve S3 and fastened rmly thereto by means of collar and set screw 90. Collet 64 is then slipped through actuating sleeve 8S and attached to hollow shaft 58 by means of externally threaded end 117.

The chuck of the present embodiment is operated in substantially the identical manner as that previously described in connection with the chuck depicted in'Figures 1 to 4.

As shown in Figure 6, the trailing end of tube 113 is first inserted into the unclamped jaws of collet 64. The knurled handle is then gripped by the operator and rotated in a direction previously determined. As the handle is rotated, it carries with it cam sleeve 97 which is prevented from rotating relative to thehandle of set screws 99. The biasing action of spring 79 urging sleeve 83 to the right as shown in Figures 5 and 6, keeps the cap of screw 85, which is attached to sleeve S3, as previously described, in rm contact against the cammed end of sleeve 97. By reason of the frictional drag developed between the cammed end of sleeve 97 and the cap of screw 85, the handles initial rotary movement carries with it 4screw S5 which in turn carries with it both cylinshaft or support member 58 which in turn carries with it collet 64. It should berunderstood that actuating sleeve or collar 88 also rotates because of its irm attachment to internal sleeve 83. Thus again,Y as in the chuck of Figures l `to 4, as the operator initially rotates handle 92, the entire chuck assembly also rotates.

In normal operation a stop is provided, after the handle has been rotated to a certain plane of bend, which prevents further rotation of hollow shaft 58 and its associated parts. The operator, however continues to rotate the handle causing the cammred end of sleeve 97 to rotate relative to the cap of screw 85. Thus as the handle and sleeve rotate, screw reciprocates longitudinally in slot 77, carrying with it sleeve 83 and actuating sleeve 8,8. With the chuck initially in the position shown in Figure 6, as the handle is rotated the screw moves to the right causing the actuating sleeve to move longitudi- Y nally relative to collet 64 thus causing the collet jaws to iirmly clamp the trailing end of the tube.

After the bending operation has been completed as previously described, and it is time to release the tube, the operator continues to move the handle in the same direction as that used to clamp the tube. Again the cammed sleeve rotates relative to the head of screw 85, the cam being so designed that such relative movement causes sleeve 83 to move back against the biasing action of spring 79, and in turn carrying with it actuatingsleeve 88, thus permitting the tube to lbe removed from the unclamped collet.

Although the now preferred embodiments of the present invention have been illustrated and described, it is to be understood that the invention need not be limited thereto for it is susceptible to changes in form and detail within the scope of the appended claims.

I claim:

l. A tube chuck for a tube bending machine comprising: a tubular housing member with a protuberance free external configuration formed with an internal bore therein; a support member rotatably mountedwithin said tubular housing having a iirst end adapted for attachment to said machine and a second end provided with a collet; actuating means carried by said support member and longitudinally movable with respect to said collet in one direction to surroundingly engage said collet moving portions of it radially inwardly to cause it to grip a tube end and longitudinally movable in the opposite direction to disengage from said collet to permit it to release said tube end; irst camming means `carried by said actuating means; spring ybiasing means carried bysaid support member and engaging said actuating means to urge said actuating means in said one direction; and second camming means carried by said tubular housing member rotatable in one direction with respect to said tirst camming means to thereby urge said actuating means in the opposite direction against the force of said spring biasing means,

.and rotatable further in the same direction to thereby enable said actuating means to move in said one direction urged by said spring biasingmeans.

' 2. A device for Aretaining a tube in position ina bending machine comprising: a support member adapted at one end for attachment to said machine and provided at the opposite end with a radially movable gripping jaw; actuating means longitudinally movable on said support member in one direction to surroundingly engage said gripping jaw moving portions thereof radially inwardly to cause said gripping jaw to grip a tube end and said actuf ating means longitudinally movable in the opposite diy rection to disengage from said surrounding engagement with said gripping jaw to permit it to release said tube end; spring VmeansV carried by said support member contacting said actuating means urging it in the direction causing said gripping jaw to grip said tube end; a rotatable vhousing member with a protuberance tree/external Configuration mounted upon said support member; camming carried by said housing member contacting a portion of said actuating means and rotatable relative to said actuating means and operative when rotated in one direction relative to said actuating means to move said actuating means in said opposite direction against the biasing action of said spring means to disengage said actuating means from surrounding engagement with said gripping jaw to permit said tube end to be removed, and said housing member operative when further rotated in said i0 one direction to cause said spring means to move said actuating means in the direction causing said gripping jaw to grip said tube end.

References Cited in the le of this patent UNITED STATES PATENTS 2,370,729 Hoppe Mar. 6, 1945 2,475,519 Robichaud July 5, 1949 10 2,655,826 Goldsby Oct. 20, 1953 

